A method and an apparatus according to an embodiment of the invention includes a reflector and an optical fiber end portion disposed within a capillary for use in side-firing optical fibers. The reflector surface can be coated with a multilayer dielectric coating to increase the amount of side-fired laser energy. An outer member or cap can be used to protect the capillary when being inserted through a catheter or endoscope. The endoscope is then at least partially inserted into a patient's body to provide laser-based medical treatment. Multiple grooves can be defined on an outer surface of the optical fiber buffer layer to increase the surface area and improve the mechanical strength of the coupling between the optical fiber and the capillary. In some embodiments, the outer member or cap can also be coupled to the grooved surface portion of the optical fiber buffer layer.